One thing I find rather amazing about all of this is the degree to which the Bitcoin community has tried, for years, to claim that quantum computers will be another other than a complete break.

Sure, it takes a pretty nice quantum computer or a pretty good algorithm or a degree of malice on the part of miners to break pay-to-script-hash if your wallet has the right properties, but that seems like a pretty weak excuse for the fact that the entire scheme is broken, completely, by QC.

Does there even exist a credible post-quantum proof protocol that could be used to “rescue” P2SH wallets?

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ViscountPenguin an hour ago | parent | next [-]

Call me crazy, but I think if bitcoin is ever broken they're more likely to move to a centralized ledger than a more secure decentralized ledger. Roughly nobody invested in bitcoin cares about the original mission, they just care about their asset prices.

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Strilanc 3 hours ago | parent | prev | next [-]

The best proposal I have heard for rescuing P2SH wallets after cryptographically relevant quantum computers exist is to require vulnerable wallets to precommit to transactions a day ahead of time. The precommitment doesn't reveal the public key. When the public key must be exposed as part of the actual transaction, an attacker cannot redirect the transaction for at least one day because they don't have a valid precommitment to point to yet.

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warkdarrior 3 hours ago | parent [-]

24-hour latency to make a payment? What is this, the 20th century?

	▲	Strilanc 2 hours ago \| parent [-]
		This is for rescue, not for payment. Once you've moved the coins to quantum-secure wallet, the delay would no longer be needed. ...probably some people would be very inconvenienced by this. But not as inconvenienced as having the coins stolen or declared forever inaccessible.

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int32_64 2 hours ago | parent | prev | next [-]

> the Bitcoin community has tried, for years, to claim that quantum computers will be another other than a complete break.

Who specifically is claiming this? Satoshi literally mentioned the need to upgrade if QC is viable on bitcointalk in 2010.

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bawolff 3 hours ago | parent | prev | next [-]

On the brightside at least we'll have a clear indicator for when quantum computers actually arrive.

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Mistletoe 2 hours ago | parent | prev [-]

If Bitcoin is broken then your bank encryption and everything else is broken also.

As far as I know quantum computers still can't even honestly factor 7x3=21, so you are good. And the 5x3=15 is iffy about how honest that was either.

https://news.ycombinator.com/item?id=45082587

Bitcoin uses 256-bit encryption, it's a universe away from 5x3=15.

	▲	Strilanc 2 hours ago \| parent [-]
		You are assuming that progress on factoring will be smooth, but this is unlikely to be true. The scaling challenges of quantum computers are very front-loaded. I know this sounds crazy, but there is a sense in which the step from 15 to 21 is larger than the step from 21 to 1522605027922533360535618378132637429718068114961380688657908494580122963258952897654000350692006139 (the RSA100 challenge number). Consider the neutral atom proposal from TFA. They say they need tens of thousands of qubits to attack 256 bit keys. Existing machines have demonstrated six thousand atom qubits [1]. Since the size is ~halfway there, why haven't the existing machines broken 128 bit keys yet? Basically: because they need to improve gate fidelity and do system integration to combine together various pieces that have so far only been demonstrated separately and solve some other problems. These dense block codes have minimum sizes and minimum qubit qualities you must satisfy in order for the code to function. In that kind of situation, gradual improvement can take you surprisingly suddenly from "the dense code isn't working yet so I can't factor 21" to "the dense code is working great now, so I can factor RSA100". Probably things won't play out quite like that... but if your job is to be prepared for quantum attacks then you really need to worry about those kinds of scenarios. [1]: https://www.nature.com/articles/s41586-025-09641-4